SEDIMENTATION ANALYSIS OF ICE CONTACT DELTAS IN CONCORD, MASSACHUSETTS

We employed ground-penetrating radar (GPR), shallow seismic imagery, and textural and mineralogical analyses of sediment cores to investigate the internal structure, sedimentology, and detailed origin of ice contact deltas formed alongside the Laurentide Ice Sheet in Glacial Lakes Concord and Sudbury. We constructed digital terrain models (DTM) from stereoscopic analyses of historical and modern aerial photographs to aid in identifying the areal extent of deltas. Shallow seismic imagery indicates that the measured delta of Glacial Lake Sudbury is 18 m and that shallow bedrock highs likely provided pinning points for ice-sheet stabilization during deglaciation. Five kilometers of ground-penetrating radar (GPR) using a 200 MHz antenna set at 200 and 300 ns achieved depths of up to 15 m and delineated foreset beds, paleochannels, and numerous faults associated with ice fluctuations and collapse upon margin retreat. Textural analyses from cores in deltaic and distal-lacustrine beds, along with GPR records indicate that Holocene dissection of the deltas via groundwater sapping is likely controlled by textural changes associated with the location and character of buried paleochannels. Digital terrain models help quantify the volume of sediment lost due to ground water sapping and to predict future changes in delta morphology.